Electromagnetic devices known as contactors and starters are frequently connected in control circuits and are used in circuits known as branch circuits to control the energization of an electric load, such as an electric motor. Various code requirements dictate that these branch circuits, as well as the control circuit, be protected by overcurrent devices which will interrupt the circuit whenever an excess current flows through the circuit. These overcurrent devices may include fuses, circuit breakers, or both.
Fuse holders which are suitable for incorporation into such branch or control circuits are well known. An illustration of one such fuse holder that is particularly suited for use in control circuits is disclosed in U.S. Pat. No. 3,732,516, which was granted on May 8, 1973, to Jordan S. Puetz and assigned to the assignee of the present invention. Such fuse holders as disclosed in the Puetz patent were designed to accept lower ampere rated fuses, such as standard 600-volt, 6-amp maximum fuses having standardized physical dimensions.
As the available current supply to electric utilization installations is constantly increasing, it is required that fuse manufacturers develop control circuit fuses which are capable of interrupting higher currents, e.g., 200,000 amperes. To meet this requirement, fuse manufacturers are offering fuses which have the same physical dimensions as other standardized control circuit fuses with a much lower interrupt rating. Thus, to a degree, standard rated fuses and fuses having higher interrupting capability are interchangeable. This interchangeability feature was convenient for users, but created other problems. A user who had a need for a fuse capable of interrupting 200,000 amperes could not be sure that a fuse which was incapable of interrupting 200,000 amperes could not be substituted. Fuse manufacturers currently are producing fuses with a 200,000 ampere interrupt rating which incorporate a rejection feature.